CN103023500A - Analog-to-digital converter - Google Patents

Analog-to-digital converter Download PDF

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Publication number
CN103023500A
CN103023500A CN2012102241766A CN201210224176A CN103023500A CN 103023500 A CN103023500 A CN 103023500A CN 2012102241766 A CN2012102241766 A CN 2012102241766A CN 201210224176 A CN201210224176 A CN 201210224176A CN 103023500 A CN103023500 A CN 103023500A
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China
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mtj element
analog
resistance value
variable
digital converter
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CN103023500B (en
Inventor
丸亀孝生
棚本哲史
木下敦宽
井口智明
铃木正道
齐藤好昭
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Toshiba Corp
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Toshiba Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/10—Calibration or testing
    • H03M1/1009—Calibration
    • H03M1/1033—Calibration over the full range of the converter, e.g. for correcting differential non-linearity
    • H03M1/1057—Calibration over the full range of the converter, e.g. for correcting differential non-linearity by trimming, i.e. by individually adjusting at least part of the quantisation value generators or stages to their nominal values
    • H03M1/1061—Calibration over the full range of the converter, e.g. for correcting differential non-linearity by trimming, i.e. by individually adjusting at least part of the quantisation value generators or stages to their nominal values using digitally programmable trimming circuits
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12—Analogue/digital converters
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B61/00—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N50/00—Galvanomagnetic devices
    • H10N50/10—Magnetoresistive devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N59/00—Integrated devices, or assemblies of multiple devices, comprising at least one galvanomagnetic or Hall-effect element covered by groups H10N50/00 - H10N52/00
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12—Analogue/digital converters
    • H03M1/34—Analogue value compared with reference values
    • H03M1/36—Analogue value compared with reference values simultaneously only, i.e. parallel type
    • H03M1/361—Analogue value compared with reference values simultaneously only, i.e. parallel type having a separate comparator and reference value for each quantisation level, i.e. full flash converter type
    • H03M1/362—Analogue value compared with reference values simultaneously only, i.e. parallel type having a separate comparator and reference value for each quantisation level, i.e. full flash converter type the reference values being generated by a resistive voltage divider
    • H03M1/365—Analogue value compared with reference values simultaneously only, i.e. parallel type having a separate comparator and reference value for each quantisation level, i.e. full flash converter type the reference values being generated by a resistive voltage divider the voltage divider being a single resistor string

Abstract

The invention relates to an analog-to-digital converter. According to an embodiment, an analog-to-digital converter includes a voltage generating unit, and a plurality of comparators. The voltage generating unit is configured to divide a reference voltage by a plurality of variable resistors to generate a plurality of comparative voltages. Each of the plurality of comparator is configured to compare any one of the plurality of comparative voltages with an analog input voltage and output a digital signal based on a result of a comparison between the comparative voltage and the analog input voltage. Each of the plurality of variable resistors includes a plurality of variable resistive elements that are connected in series, and each of the plurality of variable resistive elements has a resistance value that is variably set according to an external signal.

Description

Analog to digital converter
The cross reference of related application
The application is based on the Japanese patent application No.2011-206961 that submitted on September 22nd, 2011 and require its senior interest; By reference its full content is incorporated in this.
Technical field
Embodiment in this explanation relates in general to analog to digital converter.
Background technology
Analog to digital converter (AD converter) is categorized into three types roughly: successive approximation, parallel relatively type and Delta Sigma (△ ∑) type.Among these types, parallel relatively type also is known as flash-type (flash type), and can utilize (2 n-1) individual comparative voltage and (2 n-1) individual comparator is to be used for that the full size (full scale) of analog signal is divided into 2 nIndividual segmentation come single relatively in the acquisition digital value.For this reason, walk abreast comparison A/D converter with high speed operation.
Yet known parallel relatively type has the large problem of circuit size.Reason is as follows.AD converter comprises three kinds of primary elements: the resistor ladder (resitor ladder), comparator group and the encoder that are used for generating comparative voltage.The conversion accuracy of AD converter is decided according to the precision of resistor ladder and the resolution of comparator, and along with circuit area increases described precision or resolution raising.
Also namely, in parallel relatively type, circuit size increases to exchange for the improvement of conversion accuracy.In other words, be difficult to utilize little circuit area to realize high-resolution.
In order to realize high-resolution, must improve the dividing potential drop precision of resistor ladder.Usually, the precision of resistor ladder depends on the precision of semiconductor microactuator manufacturing technology.As a kind of method of avoiding this, used a kind of like this method, wherein, form resistive fuse (variable resistance) with the resistor ladder, and before shipment by laser irradiation seriatim the fusing resistor fuse come adjusting resistance value.
Yet along with the increase of resolution, circuit size increases.Therefore, in above-mentioned method, at circuit and another circuit with the SOC(system on chip) the form attended operation time, be difficult to seriatim adjusting resistance value.For this reason, the resolution of AD converter finally is limited to the scope of the precision of semiconductor microactuator manufacturing technology.In addition, in case the resistive fuse fused, then after this can not adjusting resistance value.Therefore, the dividing potential drop precision of resistor ladder is difficult to improve.
Summary of the invention
The purpose of embodiment provides and a kind ofly can realize that high conversion accuracy suppresses the analog to digital converter of circuit size simultaneously.
According to an embodiment, analog to digital converter comprises voltage generating unit and a plurality of comparator.Voltage generating unit is configured to come reference voltage is carried out dividing potential drop to generate a plurality of comparative voltages by a plurality of variable resistances.In described a plurality of comparator each is configured to any one and analog input voltage in described a plurality of comparative voltages are compared, and based on the comparative result output digit signals between described comparative voltage and the described analog input voltage.In described a plurality of variable resistance each comprises a plurality of variable resistor elements that are connected in series, and in described a plurality of variable resistor element each has the resistance value that arranges changeably according to external signal.
According to above-mentioned analog to digital converter, can realize high conversion accuracy, suppress simultaneously circuit size.
The specific embodiment mode
Describe below with reference to the accompanying drawings the example (being called in the following description " AD converter ") according to the analog to digital converter of embodiment in detail.
The AD converter of this embodiment is a kind of parallel relatively AD converter of type (flash-type).At first, with parallel relatively principle and the resolution of the AD converter 1 of type in the key diagram 1.As shown in fig. 1, AD converter 1 comprises voltage generating unit 2, a plurality of comparator 3 and encoder 4.Voltage generating unit 2 comprises a plurality of resistor R(resistor ladders that are connected in series).The reference voltage V of voltage generating unit 2 by utilizing the resistor ladder that the outside is applied REFCarry out dividing potential drop and generate a plurality of comparative voltages.Described a plurality of comparative voltages that voltage generating unit 2 generates are imported into corresponding comparator 3.Analog input signal (input voltage) jointly is input to described a plurality of comparator 3.In the comparator 3 each compares comparative voltage and the analog input voltage of input, and based on the as a result output digit signals of the comparison between described comparative voltage and the analog input voltage to encoder 4.The digital value of encoder 4 outputs by the encoding digital signals from comparator 3 outputs is obtained.
Partly show the number of resistor R and comparator 3 among Fig. 1.Along with the increase of the number of resistor R and comparator 3, resolution is enhanced.With regard to the improvement of the conversion accuracy of AD converter, the expectation AD converter has 10 or larger resolution.Yet, for ease of the explanation, the below explanation is had less bits resolution AD converter as an example.
From by dividing equably reference voltage V REFScope (in the situation that 8 be divided into 256 and in the situation that 10 be divided into 1024) and the integer value that the value that obtains obtains is read as the output valve (digital value of conversion) from AD converter 1.In addition, " V REF" or " ± V REF" can apply as reference voltage.Applying " V REF" time, in step-like I/O (I/O) characteristic shown in Fig. 2, by with " V REF" represent the figure place of output valve divided by 2N(N) and value (that is, the V that obtains REF/ 2N) height corresponding to a step (is applying " ± V REF" time be 2V REF/ 2N)).In this case, the number of step is " 2 N-1 ".For example, in the situation that 3, analog input voltage is divided into 8(=2 3), and the number of step is 7, as shown in Figure 2.The voltage level that comprises no-voltage is output as described digital value.Using minimum voltage unit as the LSB(least significant bit) time, only LSB has the scope of 1/2LSB.LSB refers to the least significant digit in the binary number originally.On the other hand, the most significant digit of binary number is known as MSB.AD converter 1 is with analog input voltage and pass through the resistor ladder to reference voltage V REFIn the branch pressure voltage that carries out dividing potential drop and obtain each compares, thereby obtain the as a comparison output of device of thermometer code (thermometer code), and convert described thermometer code to binary code by encoder 4, and export described binary code (numeral output).
The voltage ratio precision that the precision of AD converter 1 is carried out according to each comparator 3 is decided.For example, in the situation that 8, from it is applied " ± V REF=± 0.5V " the comparative voltage of resistor ladder output between the little value that is spaced apart 4mV.The maximum of step-like voltage error need to be suppressed to 2mV(1/2LSB) or less.In the situation that utilize the CMOS technology, the resistor ladder utilizes polysilicon to be manufactured on the place of Si substrate (such as the SiO of LOCOS or STI usually 2Insulated part) on.In order to increase processing accuracy, can form pseudo-resistor in the position of next-door neighbour's resistor ladder.In addition, the Joule heat of resistor generation may affect differential non-linearity errors (DNL) or integral non-linear error (INL).For fear of the impact of the heat that generates from substrate, if not at the FEOL(of Si substrate front end processing procedure) upper and the BEOL(rear end processing procedure on interlayer dielectric of layer) layer formation variable resistance, then do not have problems.
When having the affecting of DNL, the step-like line of Fig. 2 (line of expression I/O characteristic) is by horizontal-shift.The integration of the impact of DNL causes the form of a kind of INL of being known as, and wherein all parts fluctuate with stepped form.Typically, AD converter 1 needs manufacturedly realize high-resolution and the impact of DNL and INL is suppressed to 1/2LSB or less.In addition, reference voltage V REFPrecision or stability the reliability of the value of AD converter is had large impact.Therefore, in this embodiment, suppose for example to use general bandgap voltage reference as reference voltage in the cmos circuit, and for reference voltage V REFGuarantee the high accuracy of 1 or lower error.
Aforesaid, the performance of parallel comparison A/D converter is decided according to the precision of input voltage.Especially, in order to realize high-resolution, the dividing potential drop precision of resistor ladder is important.Thus, in this embodiment, the resistor ladder is configured with a plurality of variable resistances, and each variable resistance has the resistance value that arranges changeably according to external signal.The below will be specifically described.
Fig. 3 shows the block diagram according to the illustrative arrangement example of the AD converter 100 of this embodiment.As shown in Figure 3, AD converter 100 comprises voltage generating unit 10, comparator group 20, encoder 30 and rewritting circuit 40.At this, with the example of explanation comprising the AD converter 100 of rewritting circuit 40, but AD converter 100 is not limited to such configuration.For example, AD converter 100 can not comprise rewritting circuit 40.In this case, the packaged chip of AD converter 100 can comprise the terminal that will be connected with voltage generating unit 10, comparator group 20, encoder 30 and rewritting circuit 40.Even this permission is after AD converter 100 is manufactured, AD converter also can be connected with rewritting circuit 40 by described terminal, and can carry out neatly resistance adjustment (will illustrate after a while).
Fig. 4 is the figure for the detailed configuration of explanation AD converter 100.In Fig. 4, not shown rewritting circuit 40.As shown in Figure 4, voltage generating unit 10 comprises a plurality of variable resistance Rv that are connected in series.The reference voltage V that voltage generating unit 10 utilizes a plurality of variable resistance Rv that the outside is applied REFCarry out dividing potential drop, thereby generate a plurality of comparative voltages.Among the described variable resistance Rv each comprises a plurality of variable resistor element rj that are connected in series.Among the variable resistor element rj each has the resistance value that arranges changeably according to external signal.Details will be in after a while explanation.
Comparator group 20 shown in Fig. 3 comprises a plurality of comparators 21.A plurality of comparative voltages that voltage generating unit 10 generates are imported into corresponding comparator 21.Analog input signal (input voltage) jointly is input to described comparator 21.In the comparator 21 each with the input comparative voltage and described analog input voltage compare, and based on the comparison as a result output digit signals to encoder 30.The digital value of encoder 30 outputs by the encoding digital signals from comparator 21 outputs is obtained.Driving voltage Vdd is supplied to comparator 21 and encoder 30.
Then, with the variable resistor element rj that comprises among the explanation variable resistance Rv.For example, in this embodiment, variable resistor element rj comprises magnetoresistance element.Magnetoresistance element forms technique and little manufacturing process manufacturing by film.Magnetoresistance element layer resistivity with identical film type is almost identical.At this, as example of magnetoresistance element magnetic tunnel-junction (below be called " MTJ ") element is described.Hereinafter, variable resistor element rj is called " MTJ element rj ".
As shown in Figure 5, MTJ element rj has the three-decker of magnetic film 11, tunnel insulator film 12 and magnetic film 13.For example, can adopt CoFeB as magnetic film 11, can adopt MgO as tunnel insulator film 12, and can adopt CoFeB as magnetic film 13.
In the example of Fig. 5, the magnetic film 11 that is in downside is variable magnetization free layer of the direction of magnetization wherein.IrMn as antiferromagnet is deposited on the magnetic film 13 that is in upside, forms the wherein immutable magnetization fixed layer of the direction of magnetization.When the direction of magnetization of the direction of magnetization of magnetization free layer (magnetic film 11) and magnetization fixed layer (magnetic film 13) is identical (in the situation that magnetization is parallel), the resistance of MTJ element rj becomes low-resistance value, as shown in Figure 5.Yet when the direction of magnetization of the direction of magnetization of magnetization free layer and magnetization fixed layer is opposite (in the antiparallel situation of magnetization), the resistance of MTJ element rj becomes high resistance, as shown in Figure 5.Aforesaid, the resistance value of MTJ element rj is changed into any one in two types the resistance value (high resistance and low-resistance value) according to the magnetized state of MTJ element rj.
The ratio of the resistance value when magnetizing resistance value (low-resistance value) when parallel with the magnetization antiparallel is known as magnetoresistance ratio (mr) (below, be called " MR ratio ") and is defined by following formula (1):
MR ratio=(high resistance-low-resistance value)/(low-resistance value) (1)
For example, along with the magnetization the parallel magnetization antiparallel that becomes, when resistance value had changed twice (also namely, high resistance is that the twice of low-resistance value is large), the MR ratio became 100%(" 1 ").For example, when resistance value had changed ten times, the MR ratio became 900%(" 9 ").In the situation that the MTJ element, can easily make the element that at room temperature has 100% MR ratio.
Each thickness in magnetic film 11, tunnel insulator film 12 and the magnetic film 13 is set to obtain the MR ratio of expectation.For example, at CoFeB(magnetic film 11 and 13) thickness be set to approximately 3nm and MgO(tunnel insulator film 12) thickness when being set to approximately 1nm, obtain approximately 10 Ω mm 2Sheet resistance RA and about 100% MR ratio.These values become according to film formation condition and follow-up heat treated, and therefore manufacturer need to set in advance condition.Yet MTJ has such feature, that is, in case obtain, the reproducibility of MR ratio or RA is very high.As shown in Figure 5, the resistance of MTJ becomes according to the external magnetic field, and in the situation that magnetization is parallel and in the antiparallel situation of magnetization, resistance value has binary condition significantly.
The material of magnetic film is not limited to CoFeB, and can comprise alloys such as comprising Fe or Co.MR ratio in order to obtain to expect can use the high spin-polarization material, such as Heusler alloy or oxidate magnetic material.Tunnel insulator film is not limited to MgO, and can use the tunnel insulator film such as AlOx, as long as obtain the MR ratio of expectation.The type that is used for the fixing antiferromagnetic film of magnetization is not limited to IrMn, and free layer and fixed bed can be reversed.Can adopt known MRAM or HDD to read the configuration of the MTJ of first-class middle formation.
After determining the thickness of each film in above-mentioned mode and carrying out film formation, carry out the little manufacturing processing that is used for determining size, thus the MTJ element rj that formation is connected in series.In the example of Fig. 6, three kinds of MTJ element rj A1, A2 and A3 with different size have been formed.Among the described MTJ element rj each deposits by single film forming.Fig. 7 shows the view of watching from the top of the film after processing.In this example, the area of A2 is that the twice of A1 is large, and the area of A3 be four times of A1 large.Area at A1 is 1 o'clock, and the area of A2 is 2, and the area of A3 is 4.Alternatively, as shown in Figure 8, can utilize a1 to utilize the number definition area of a1 as unit are.For example, a2 is 2 a1, and a3 is 4 a1.In this case, MTJ element rj must not need to be closely adjacent to each other until the limit, and can be arranged to the distance that each other maintenance does not exert an influence to processing.By this way, can suppress the impact of the process-induced damage of the impact of technique change or MTJ element rj marginal portion.MTJ element rj by before forming described MTJ element rj and interconnection afterwards form technique and be connected in series (see figure 6).By this way, form a plurality of MTJ element rj that be connected in series and that have different area.
Then, explanation is regulated the method for the resistance value of variable resistance Rv.Rewritting circuit 40 shown in Fig. 3 arranges the resistance value of each variable resistance Rv changeably according to external signal.In this embodiment, when being applied to the MTJ element rj that is included among the variable resistance Rv in the magnetic field that generates owing to the electric current that flows through the corresponding signal line, the magnetized state of MTJ element rj changes (resistance value change).Rewritting circuit 40 arranges the resistance value of MTJ element rj changeably by the electric current that flows through holding wire according to the external signal control of input.The below will carry out more specifically bright.
As shown in Figure 9, in this embodiment, the crosspoint of a plurality of bit lines 102 that extend in parallel with a plurality of word lines 101 that extend in parallel in the row direction with at column direction forms a plurality of MTJ element rj accordingly.In the example of Fig. 9, each among a plurality of variable resistance Rv that are connected in series comprises 7 MTJ element rj that are connected in series.
Rewritting circuit 40 changes the magnetized state of the MTJ element rj corresponding with word line 101 and bit line 102 by the electric current (control sense of current or value) that flows through word line 101 and bit line 102 according to external signal control.In this example, (from the magnetic field that word line 101 and bit line 102 are revealed to the outside) when being applied to MTJ element rj, the magnetized state of MTJ element rj changes in magnetic field that the electric current that flows through corresponding word line 101 and corresponding bit line 102 owing to electric current generates.
In the example of Fig. 9, a plurality of MTJ element rj are by with matrix arrangement, but the present invention is not limited to this.For example, can form accordingly with the crosspoint of a word line 101 and a plurality of bit line 102 a plurality of MTJ element rj.Alternatively, for example, can form accordingly with the crosspoint of a bit line 102 and a plurality of word lines 101 a plurality of MTJ element rj.In other words, if each MTJ element rj can be arranged to close to word line 101 and the bit line 102 corresponding with this MTJ element rj, and can control changeably the magnetized state of this MTJ element rj when being applied to this MTJ element rj in the magnetic field that generates owing to the electric current that flows through the word line 101 corresponding with this MTJ element rj and bit line 102, just be enough to.
In the example of Fig. 9, in advance each MTJ element rj is externally applied reset magnetic field, thereby each MTJ element rj is arranged (resetting) to the magnetization parastate.For the MTJ element rj that is specified " magnetization antiparallel " (it will illustrate after a while) by the external signal of input, control carried out by rewritting circuit 40 so that predetermined electric current flows to the word line 101 corresponding with the MTJ element rj that considers and each in the bit line 102.For example, in Fig. 9, at " magnetization antiparallel " designated conduct and word line 101[2 from the second row the top] and from the right side the bit line 102[3 the 3rd row] MTJ element rj[2 corresponding to crosspoint, during 3] magnetized state, control carried out by rewritting circuit 40 so that predetermined electric current flows to the word line 101[2 of the second row] and tertial bit line 102[3] in each, as shown in Figure 9.At this moment, owing to the word line 101[2 that flows through the second row] and tertial bit line 102[3] the magnetic field (resultant magnetic field) that generates of electric current be applied to MTJ element rj[2,3] magnetized state, so this MTJ element rj[2,3] is from magnetizing the parallel magnetization antiparallel that becomes.
The above embodiments are examples, and can the magnetized state of MTJ element rj be changed into magnetization parastate or anti-parallel states of magnetization with method arbitrarily.For example, rewritting circuit 40 can flow through the electric current of word line 101 and bit line 102 and not use from the reset magnetic field of outside the magnetized state of each MTJ element rj is resetted (resetting individually) to the magnetization parastate by control individually.
The external signal that is input to rewritting circuit 40 comprises with the man-to-man mode a plurality of control signals corresponding with described a plurality of variable resistance Rv.Each control signal is by a plurality of bit representations, and described a plurality of positions are corresponding with the described a plurality of MTJ element rj that comprise among man-to-man mode and the corresponding variable resistance Rv.Be set to any one of (high resistance and low-resistance value) in two types the resistance value according to corresponding with the MTJ element rj that considers each MTJ element rj of position.
To illustrate that now as shown in Figure 10 a variable resistance Rv comprises the example of three MTJ element rj1 to rj3 that are connected in series.In the example of Figure 10, suppose that the size (forming the area value of the film of this MTJ element) of MTJ element rj1 is A1, the size of MTJ element rj2 is A2, and the size of MTJ element rj3 is A3.Because resistance value and area value are inversely proportional to, so when MTJ element rj1 has identical magnetized state with rj2, the resistance value of MTJ element rj1 is that the twice of resistance value of MTJ element rj2 is large.In addition, the resistance value of MTJ element rj1 is that four times of resistance value of MTJ element rj3 are large.
The control signal corresponding with the variable resistance Rv shown in Figure 10 is by 3 bit representations, and the 3rd (highest significant position) from least significant bit is corresponding to the MTJ element rj1 with maximum resistance.In addition, the second from least significant bit is corresponding to the MTJ element rj2 with second largest resistance value.In addition, the first bit from least significant bit is corresponding to the MTJ element rj3 with minimum resistance.
According to 3 the control signal corresponding with the variable resistance Rv of Figure 10, rewritting circuit 40 arranges the resistance value of variable resistance Rv changeably.In the example of Figure 10, when the position corresponding with MTJ element rj is " 1 ", because the magnetized state of the MTJ element rj of " magnetization antiparallel " designated conduct, so rewritting circuit 40 controls are flow through the electric current of word line 101 and bit line 102 so that the magnetized state of MTJ element rj is changed into the magnetization antiparallel.As a result, the resistance value of MTJ element rj is set to high resistance.When the position corresponding with MTJ element rj is " 0 ", because " magnetize parallel " designated magnetized state as MTJ element rj, thus rewritting circuit 40 controls flow through word line 101 and bit line 102 electric current so that the magnetized state of MTJ element rj change into magnetize parallel.As a result, the resistance value of MTJ element rj is set to low-resistance value.Yet the present embodiment is not limited to this example.For example, when the position corresponding with MTJ element rj is " 1 ", " magnetizing parallel " can be specified the magnetized state as MTJ element rj, and when being " 0 " in the position corresponding with this MTJ element rj, " magnetization antiparallel " can be appointed as the magnetized state of this MTJ element rj.In other words, if be set in two types the resistance value (high resistance and low-resistance value) any one according to corresponding with MTJ element rj each MTJ element rj of position, so just be fine.
The resistance value of the variable resistance Rv of Figure 10 is represented by following formula (2):
Resistance value=Rp * ∑ (the 1+MR ratio * aj) * 2 N(2)
In formula (2), Rp is illustrated in the sheet resistance in the parallel situation of magnetization.In addition, aj represents the magnetized state with MTJ element rj corresponding to j position from least significant bit (in this example, 1≤j≤3).In the situation that the parallel aj of magnetization is set to " 0 ", but in the antiparallel situation of magnetization, be set to " 1 ".N(in this example, 0≤N≤2) expression bit position (weight).For example, suppose that Rp is per unit area 1 Ω, the MR ratio is 100%, and the control signal corresponding with the variable resistance Rv of Figure 10 is " 101 ".In this case, the electric current of word line 101 and bit line 102 is flow through in rewritting circuit 40 controls, so that the magnetized state of MTJ element rj1 becomes " magnetization antiparallel ", the magnetized state of MTJ element rj2 becomes " magnetizing parallel ", and the magnetized state of MTJ element rj3 becomes " magnetization antiparallel ".The resistance value of the variable resistance Rv of Figure 10 becomes 12 Ω (=1 * { (1+100% * 1) * 2 2+ (1+100% * 0) * 2 1+ (1+100% * 1) * 20}).
Aforesaid, the resistance value of the variable resistance of Figure 10 arranges changeably according to 3 control signal.Figure 11 shows the figure of the corresponding relation between the resistance value of 3 control signal and variable resistance Rv.In this example, by regulating 3 control signal, the resistance value that can regulate in the mode of stepping variable resistance Rv.
Aforesaid, in this embodiment, the resistor ladder of AD converter 100 comprises a plurality of variable resistance Rv, and each variable resistance Rv has the resistance value that arranges changeably according to external signal.Therefore, even also can adjusting resistance value after AD converter is manufactured.In addition, each variable resistance Rv comprises a plurality of MTJ element rj that are connected in series, and each MTJ element rj has the resistance value that arranges changeably according to external signal (control signal).Therefore, can regulate in the mode of stepping the resistance value of each variable resistance Rv.Therefore, owing to the dividing potential drop precision that can improve the resistor ladder need not to provide fuse etc., the conversion accuracy that therefore can improve AD converter 100 suppresses the increase of circuit size simultaneously.
In addition, in this embodiment, forming the film be comprised in the described a plurality of independent MTJ element rj among the variable resistance Rv is different (be different in resistance values) at area value).Therefore, compare with the situation that wherein forms the film be comprised in a plurality of independent MTJ element rj among the variable resistance Rv and be set to have identical area value, have following advantage: the resistance value that can regulate variable resistance Rv in the mode that multistep is more advanced.
Then, a plurality of modified examples will be described.The modified example that the following describes can at random make up.
(1) first modified example
In the above-described embodiment, each variable resistance Rv comprises a plurality of variable resistor elements (for example, the MTJ element) rj that is connected in series, but the invention is not restricted to this.For example, each variable resistance Rv can comprise fixed resistor Rs and a plurality of variable resistor element rj that is made by polysilicon, and it is connected in series, as shown in Figure 12.In other words, if each variable resistance Rv comprises a plurality of variable resistor elements that are connected in series, and each variable resistor element has the resistance value that arranges changeably according to external signal, so just is fine.For example, suppose polysilicon (fixed resistor Rs) and a plurality of total resistance values of 1k Ω to be set to the variable resistor element rj combination of 1 Ω in order to realize 1.1k Ω as the resistance value of the variable resistance Rv among Figure 12.In this case, if even find that after making polysilicon has 1% technique change and variable resistance Rv and has the resistance value of 999 Ω, also can be by external signal is set so that the resistance value of a plurality of variable resistor element rj to be changed into 2 Ω from 1 Ω, the total resistance value of variable resistance Rv is set to 1.1k Ω.
(2) second modified examples
In the above-described embodiment, described wherein that variable resistor element rj is the example of MTJ element, but the invention is not restricted to this.For example, variable resistor element rj can be the GMR(giant magnetoresistance) element.The GMR element is different from MTJ element part and is: use nonmagnetic film to replace tunnel insulator film.In other words, the GMR element has the three-decker of magnetic film, nonmagnetic film and magnetic film.For example, can adopt Co as magnetic film, and can adopt Cu as nonmagnetic film.The material of magnetic film is not limited to Co, and can use the magnetic film of being made by the general alloy that contains Fe or Co or high spin-polarization material such as Heusler alloy or oxidate magnetic material.The material of nonmagnetic film is not limited to Cu, and can adopt such as Ag or Cr etc.Also namely, the configuration that can adopt conventional HDD to read the GMR element of first-class middle formation.
Simultaneously, owing to tunnel current flows through, so the MTJ element has non-linear I-V characteristic as shown in Figure 13.On the other hand, the GMR element has linear I-V characteristic as shown in Figure 14.In the above-described embodiment, because two or more MTJ elements are connected in series, the dividing potential drop that therefore is applied to a MTJ element reduces, and has therefore alleviated non-linear.Therefore yet for example, when analog input signal had high frequency and I-V characteristic non-linear become problem, expectation used the GMR element to replace the MTJ element.As a result, obtain the linear I-V characteristic of Figure 14.In addition, because the MJT element utilizes tunnel resistor, so the absolute value of its resistance value depends on the thickness of tunnel insulator film with exponential manner.On the other hand, wherein every one deck can easily obtain low resistance by the film formed GMR element of metal.Yet, since the GMR element MR than aspect less than MTJ element, therefore need to utilize magnetic thin film such as the Heusler alloy with high spin-polarization ratio to increase the MR ratio.
In other words, the type as the magnetoresistance element of variable resistor element rj is arbitrarily.Its resistance value that utilization resembles MTJ element or the GMR element is changed into any one magnetoresistance element in two kinds of values according to magnetized state, can realize digital control for the resistance value of controlling changeably variable resistance Rv.
(3) the 3rd modified examples
The method of controlling changeably the magnetized state of MTJ element (magnetoresistance element) is arbitrarily.For example, can use spin-injection magnetic counter-rotating (spin-injection magnetization reversal) technology, it is fed to the amplitude of electric current of MTJ element or the magnetized state that direction changes the MTJ element by control.When adopting the spin-injection magnetic inversion technique, as shown in Figure 15, be provided for optionally supplying current to the selection transistor T s of MTJ element.In this example, rewritting circuit 40 is controlled each conducting of selecting transistor T s/shutoff according to external signal, and the magnetized state of MTJ element (resistance value) changes according to the electric current of supplying by the selection transistor T s that switches to conducting state.The below will carry out more specifically bright.
Then, describe in connection with as shown in Figure 16 specific MTJ element.As shown in Figure 16, first selects transistor T s1, specific MTJ element rjx and second to select transistor T s2 to be connected in series between the first power line 111 and the second source line 112, the first current potential V1 is applied to the first power line 111, the second current potential V2 and is applied to second source line 112.First selects transistor T s1 to be disposed between the first power line 111 and the MTJ element rjx.First selects the grid of transistor T s1 to be connected to the word line 101 corresponding with MTJ element rjx.Second selects transistor T s2 to be disposed between second source line 112 and the MTJ element rjx.Second selects the grid of transistor T s2 to be connected to the bit line 102 corresponding with MTJ element rjx.In other words, selecting transistor T s is the device that whether supplies current to the switching of MTJ element rjx from power line (111 and 112) for carrying out.
Rewritting circuit 40(is not shown) change the magnetized state of MTJ element rjx by the electric current supply that controls to MTJ element rjx.For example, suppose that the electric current that flows to the predetermined amplitude of second source line 112 from the first power line 111 is supplied to MTJ element rjx.In this case, rewritting circuit 40 is at first selected the word line 101 corresponding with MTJ element rjx and bit line 102.As a result, first selects transistor T s1 and second to select transistor T s2 to change conducting state into, and therefore forms from the first power line 111 by the current path of MTJ element rjx to second source line 112.Then rewritting circuit 40 arranges the value of the first current potential V1 and the second current potential V2 so that the electric current of predetermined amplitude can flow to second source line 112(in this case from the first power line 111, V1〉V2).As a result, the electric current that flows to the predetermined amplitude of second source line 112 from the first power line 111 is supplied to MTJ element rjx, and therefore the magnetized state of MTJ element rjx changes according to this electric current.
In addition, for example, suppose that the electric current that flows to the predetermined amplitude of the first power line 111 from second source line 112 is supplied to MTJ element rjx.In this case, rewritting circuit 40 is at first selected the word line 101 corresponding with MTJ element rjx and bit line 102.Then rewritting circuit 40 arranges the value of the first current potential V1 and the second current potential V2 so that the electric current of predetermined amplitude can flow to the first power line 111(in this case from second source line 112, V2〉V1).As a result, the electric current that flows to the predetermined amplitude of the first power line 111 from second source line 112 is supplied to MTJ element rjx, and therefore the magnetized state of MTJ element rjx changes according to this electric current.
For example, when according to external signal " magnetization antiparallel " being specified magnetized state as MTJ element rjx, the conducting of rewritting circuit 40 controls the first selection transistor T s1 and the second selection transistor T s2/shutoff, and control the current potential of the first power line 111 and second source line 112, so that the magnetized state of MTJ element rjx is changed into " magnetization antiparallel ".In addition, for example, when according to external signal " magnetizing parallel " being specified magnetized state as MTJ element rjx, the conducting of rewritting circuit 40 controls the first selection transistor T s1 and the second selection transistor T s2/shutoff, and control the current potential of the first power line 111 and second source line 112, so that the magnetized state of MTJ element rjx is changed into " magnetizing parallel ".At this, described specific MTJ element rjx as example, yet can use similarly other MTJ elements rj.Figure 15 and 16 configuration are examples, and the method for attachment of word line 101 and bit line 102 is not limited to this.In other words, if adopt the configuration that the magnetized state of MTJ element rj wherein is set changeably by optionally supplying current to MTJ element rj, then this is just enough.
(4) the 4th modified examples
In the MTJ element, can comprise the random magnetism film.For example, can use have perpendicular magnetization film as magnetic film, as shown in Figure 17.In this case, can adopt vertical film that Co wherein or Fe contain Pt or Pd as magnetic film, and can adopt the vertical film that contains Gd or Tb etc. as magnetic film.As the method for controlling changeably magnetized state, can adopt as shown in Figure 17 wherein flow through the amplitude that is disposed near the electric current of writing lambda line the MTJ element or the method that direction changes the magnetized state of MTJ element by change.Also namely, by being applied to the MTJ element owing to flowing through the magnetic field (magnetic field of revealing to the outside from writing interconnection) that the electric current of writing lambda line generates, can change the magnetized state of MTJ element.Configuration is not limited to this, for example, can change by above-mentioned spin-injection magnetic inversion technique the magnetized state of MTJ element.
(5) the 5th modified examples
In the above-described embodiment, forming the film that is included in a plurality of independent MTJ element rj among the variable resistance Rv is different (being different aspect resistance value) aspect area value.Yet, the invention is not restricted to this, and form the film be included in a plurality of independent MTJ element rj among the variable resistance Rv and can be set to have identical area value.Yet, as among the above-mentioned embodiment, adopt wherein form be included in a plurality of independent MTJ element rj among the variable resistance Rv film aspect area value during different configuration, the configuration that is set to have identical area value with the film that wherein forms a plurality of independent MTJ element rj is compared, the resistance value that can regulate variable resistance Rv in the mode that multistep is more advanced.
(6) the 6th modified examples
In the above-described embodiment, described and wherein used as the MTJ element of magnetoresistance element as the example that is included in the variable resistor element rj among the variable resistance Rv.Yet the present invention is not limited to this, and the type that is used as the element of variable resistor element rj is arbitrarily.In other words, if each among described a plurality of variable resistance Rv comprises a plurality of variable resistor element rj that are connected in series, and each described variable resistor element rj has the resistance value that arranges changeably according to external signal, so just is fine.And, if consist of in a plurality of control signals of the external signal be input to rewritting circuit 40 each by a plurality of bit representations, described a plurality of position is corresponding with a plurality of variable resistor element rj in being comprised in corresponding variable resistance Rv in man-to-man mode, and be set in the resistance value in two types any one according to corresponding with variable resistor element rj each variable resistor element rj of position, so just be fine.In addition, the number of the variable resistor element rj that comprises among each variable resistor element Rv is arbitrarily, and can decide according to the resolution of the AD converter 100 of expecting to make.
According to the analog to digital converter of at least one above-described embodiment, this analog to digital converter comprises voltage generating unit and a plurality of comparator.Voltage generating unit is configured to utilize a plurality of variable resistances that reference voltage is carried out dividing potential drop, to generate a plurality of comparative voltages.In described a plurality of comparator each is configured to any one and analog input voltage in described a plurality of comparative voltages are compared, and output digit signals as a result based on the comparison.In described a plurality of variable resistance each comprises a plurality of variable resistor elements that are connected in series, and in described a plurality of variable resistor element each has the resistance value that arranges changeably according to external signal.Therefore, can realize high conversion accuracy, suppress simultaneously circuit size.
Although described some specific embodiment, these embodiment only present as example, and are not intended to limit the scope of the invention.In fact, the embodiment of novelty described here can implement with various other forms; In addition, can carry out various omissions, replacement and change in the form of described embodiment here and do not depart from spirit of the present invention.Claims and equivalent intention thereof cover these forms or the modification that will drop in the scope of the invention and the spirit.
Description of drawings
Fig. 1 shows the parallel relatively figure of the AD converter of type;
Fig. 2 shows the figure of AD converter (I/O) characteristic;
Fig. 3 shows the figure according to the illustrative arrangement example of the AD converter of an embodiment;
Fig. 4 is the figure for the detailed configuration of describing AD converter;
Fig. 5 shows the figure of the exemplary configuration of MTJ element;
Fig. 6 shows the figure of the example of a plurality of MTJ elements of form;
Fig. 7 shows the figure of the example of a plurality of MTJ elements of form;
Fig. 8 shows the figure of the example of a plurality of MTJ elements of form;
Fig. 9 is the figure for the example of the method for describing the magnetized state that changes each MTJ element;
Figure 10 shows the figure of the example of variable resistance;
Figure 11 shows the figure of the example of the corresponding relation between control signal and the resistance value;
Figure 12 shows the figure of the modification of variable resistance;
Figure 13 shows the figure of example of the I-V characteristic of MTJ element;
Figure 14 shows the figure of example of the I-V characteristic of GMR element;
Figure 15 is for the figure that describes the situation that wherein adopts the spin-injection magnetic inversion technique;
Figure 16 is be used to the figure that describes a kind of specific MTJ element; With
Figure 17 shows the figure of a kind of modification of MTJ element.

Claims (8)

1. analog to digital converter comprises:
Voltage generating unit is configured to come reference voltage is carried out dividing potential drop by a plurality of variable resistances, to generate a plurality of comparative voltages; And
A plurality of comparators, each in described a plurality of comparators are configured to any one and analog input voltage in described a plurality of comparative voltages are compared, and based on the comparative result output digit signals between this comparative voltage and the described analog input voltage,
Wherein, each in described a plurality of variable resistances comprises a plurality of variable resistor elements that are connected in series, and in described a plurality of variable resistor element each has the resistance value that arranges changeably according to external signal.
2. analog to digital converter according to claim 1,
Wherein said external signal comprises a plurality of control signals, and described a plurality of control signals are corresponding with described a plurality of variable resistances in man-to-man mode,
In the described control signal each is by a plurality of bit representations, and described a plurality of positions are corresponding with included described a plurality of variable resistor elements in the corresponding variable resistance in man-to-man mode, and
In described a plurality of variable resistor element each is set to any one in two types the resistance value according to corresponding with corresponding variable resistor element position.
3. analog to digital converter according to claim 2,
Wherein forming the film that is included in the described a plurality of variable resistor elements in the described variable resistance is different aspect area value.
4. according to claim 2 or 3 described analog to digital converters,
Wherein said variable resistor element is magnetoresistance element.
5. analog to digital converter according to claim 4,
Wherein said magnetoresistance element is magnetic tunnel junction element.
6. analog to digital converter according to claim 4,
Wherein said magnetoresistance element is giant magnetoresistive elements.
7. analog to digital converter according to claim 4 also comprises:
Rewritting circuit is configured to arrange changeably according to described external signal the resistance value of described magnetoresistance element,
When wherein being applied to described magnetoresistance element in the magnetic field that generates by the electric current that flows through the corresponding signal line, the magnetized state of magnetoresistance element changes, so that the change of the resistance value of this magnetoresistance element, and
Described rewritting circuit flows through the electric current of this holding wire according to described external signal control.
8. analog to digital converter according to claim 4 also comprises:
Rewritting circuit is configured to arrange changeably according to described external signal the resistance value of described magnetoresistance element; And
Select transistor, be configured to carry out the switching that whether electric current is fed to described magnetoresistance element from power line,
Wherein, utilize the electric current of the described selection transistor supply by being switched to conducting state to change the magnetized state of described magnetoresistance element, so that the resistance value of described magnetoresistance element changes, and
Described rewritting circuit is controlled the transistorized conducting of described selection/shutoff according to described external signal.
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